Cooling apparatus for electronic devices

ABSTRACT

A cooling system for dissipating heat from a heat source has a heat sink associated with an air moving device. The heat sink has a core member having a first surface adapted to contact at least a portion of the heat source. In addition, the core member has at least one outer peripheral surface. At least one cooling fin device having at least one inner peripheral surface and at least one cooling fin is associated with the core member wherein the inner peripheral surface of the cooling fin device is adjacent the outer peripheral surface of the core member. The air moving device is located opposite the first surface of the core member and forces air past the cooling fins in the general direction of the first surface. During operation of the cooling system, heat transfers from the heat source into the core member via the core member first surface. The core member transfers the heat to the outer peripheral surface where it is then transferred to the cooling fins. The cooling fins, in conjunction with the air of the air moving device, convect the heat to the surrounding atmosphere, thus, cooling the heat source.

FIELD OF THE INVENTION

The present invention relates generally to cooling devices and, moreparticularly, to a cooling device and method for removing heat from anelectronic device.

BACKGROUND OF THE INVENTION

Electronic components, such as integrated circuits, are increasinglybeing used in different devices. One prevalent example of a device usingintegrated circuits is the computer. The central processing unit orunits of most computers, including personal computers, is typicallyconstructed from a plurality of integrated circuits. Integrated circuitsare also used in other computer circuitry. For example, interface andmemory circuits typically comprise several integrated circuits.

During normal operation, many electronic components, such as integratedcircuits, generate significant amounts of heat. If this heat is notcontinuously removed, the electronic component may overheat, resultingin damage to the component and/or a reduction in its operatingperformance. For example, an electronic component may encounter thermalrunaway, which may damage the electronic component. In order to avoidsuch problems caused by overheating, cooling devices are often used inconjunction with electronic components.

Over the years, the amount of heat generated by electronic componentshas increased. In addition, the size of electronic devices using thesecomponents has generally decreased, resulting in greater amounts of heatbeing generated within smaller confines. In order to adequately coolthese hotter electronic devices without increasing their sizes, moreefficient cooling devices are required.

One such cooling device used in conjunction with electronic componentsis a heat sink. A heat sink is a device that draws heat from a heatgenerating component and convects the heat to the surroundingatmosphere. The heat sink is typically formed from a thermallyconductive material, such as aluminum or copper. The heat sink isusually placed on top of, and in physical contact with, the heatgenerating electronic component. This physical contact improves thethermal conductivity between the electronic component and the heat sinkand permits heat to rise from the electronic component into the heatsink. In addition, a thermally conductive compound is typically placedbetween the electronic component and the heat sink to enhance to thermalconductivity between the electronic component and the heat sink. Thisthermal conductivity results in a substantial portion of the heatgenerated by the electronic component being conducted into the heat sinkand away from the electronic component. The heat transfers to thesurface of the heat sink where it is then convected into the surroundingatmosphere.

One method of increasing the cooling capacity of heat sinks is byincluding a plurality of cooling fins attached to the heat sink and acooling fan that forces air past the cooling fins. The cooling finsserve to increase the surface area of the heat sink and, thus, increasethe convection of heat from the heat sink to the surrounding atmosphere.The fan serves to force air past the fins, which further increases theconvection of heat from the heat sink to the surrounding atmosphere.This increased convection, in turn, allows the heat sink to draw moreheat from the electronic component. In this manner, the heat sink isable to draw a significant amount of heat away from the electroniccomponent, which serves to cool the electronic component. Examples ofsuch heat sinks are disclosed in U.S. Pat. No. 5,794,685 of Dean forHEAT SINK DEVICE HAVING RADIAL HEAT AND AIRFLOW PATHS and U.S. patentapplication Ser. No. 09/253877 of Hanzlik, et al. for COOLING APPARATUSFOR ELECTRONIC DEVICES, both of which are hereby incorporated byreference for all that is disclosed therein.

The amount of heat that may be drawn from a steady state heat source isdependent on the amount of heat that may be convected into thesurrounding atmosphere. The amount of heat that may be convected intothe surrounding atmosphere is, in turn, dependent on the surface area ofthe cooling fins and other components comprising the heat sink thatconvect heat to the surrounding atmosphere. For example, cooling finswith larger surface areas are generally able to convect more heat intothe atmosphere.

Cooling fins with larger surface areas, however, tend to havesignificant barrier layers of air on the cooling fin surfaces when airis forced past the cooling fins. An air barrier is air that is adjacentthe surface of a cooling fin and remains relatively stationary relativeto the cooling fin as air is forced past the cooling fin. Thus, asignificant barrier layer of air may result in the air being forced pastcooling fins having large surface areas not being able to remove themaximum heat possible from the cooling fins. Accordingly, increasing thearea of individual cooling fins may not result in a proportional coolingcapability of the heat sink.

Another problem associated with larger cooling fins is that they occupygreater spaces, which could otherwise be used to reduce the size of theelectronic device. Larger cooling fins also occupy space that couldotherwise be used to increase the concentration of electronic componentslocated within the electronic device. As described above, electroniccomponents are being used in smaller devices, thus, a reduced space or ahigher concentration of electronic components within the electronicdevices is beneficial. The use of larger cooling fins tends to increasethe size of the electronic devices or reduce the concentration ofelectronic components located therein.

Yet another problem associated with cooling fins is that they tend to bedifficult to manufacture. For example, the cooling fins should berelatively thin in order to increase convection by providing lessrestrictive airflow past the fins. It should be noted that the thicknessof the cooling fins must be balanced against their ability to conductheat because thin cooling fins are generally unable to conduct from theheat sink as well as large cooling fins. The fin thins may, as anexample, be made from a sheet of thermally conductive metal, such as asheet of copper or aluminum. These cooling fins, however tend to bedifficult to attach to the heat sink so as to assure low thermalresistance between the cooling fins and the heat sink. They may, as anexample, be welded or brazed to the heat sink, which is relatively timeconsuming. Alternatively, the cooling fins may be integrally formed withthe heat sink. For example, the heat sink, including the cooling finsmay be molded or machined from a piece of stock. Molding or machiningthin cooling fins, however, tends to be rather difficult and costly.

Thus, it would be generally desirable to provide a cooling device thatovercomes these problems associated with conventional cooling devices.

SUMMARY OF THE INVENTION

An improved cooling device for dissipating heat from a heat source isdisclosed herein. The cooling device may comprise an elongated core madeof a thermally conductive material, such as copper or aluminum. The coremay have an outer peripheral surface and an end that may be adapted tocontact the heat source. At least one cooling fin device may be placedadjacent the outer peripheral surface of the core to enhance theconvection of heat from the core to the surrounding atmosphere. Eachcooling fin device may comprise at least one inner peripheral surfaceand at least one cooling fin associated therewith, wherein the innerperipheral surface of the cooling fin device is located adjacent theouter peripheral surface of the core. The area of the individual coolingfins may be small so as to reduce a barrier layer of air that builds upon the surface of the individual cooling fins when air is forced pastthe cooling fins. A plurality of relatively small cooling fins may beassociated with the core via the cooling fin assemblies, thus, theoverall surface area of the plurality of cooling fins may be relativelylarge, which improves convection of heat to the surrounding atmosphere.

The collars of the cooling fin devices may have inner surfaces that havesubstantially the same perimeter as the core. This allows the coolingfin devices to be pressed onto the core so as to form interference fitsbetween the cooling fin devices and the core. The interference fitsprovide low thermal resistance between the cooling fin devices and thecore, which improves the cooling capability of the cooling device byimproving the thermal conductivity between the core and the cooling findevices.

A conventional fan may be located in the vicinity of the core oppositethe heat source and may serve to force air past the surfaces of thecooling fins in order to increase convection. The fan may force air inthe general direction of the heat source in order to further increasethe cooling capability of the cooling device. A shroud may be placedover the fan and the cooling fins to assure that air blown by the fanpasses over the surfaces of the cooling fins rather than diverging fromthe core and the cooling fins.

The cooling fins may be relatively thin so as to minimize airresistance. Thus, a large quantity of air may be forced past the coolingfins, which in turn convects a large quantity of heat to the surroundingatmosphere. The cooling fins may, however, be thick enough so as to beable to draw a significant amount of heat from the core.

When the cooling device is used to dissipate heat generated by a heatgenerating electronic component mounted to a circuit board, the core isplaced adjacent the electronic component. Heat is drawn from theelectronic component into the core and away from the electroniccomponent. The heat then transfers to the surface of the core and to thecooling fins. The air forced past the cooling fins by the fan convectsthe heat to the surrounding atmosphere, thus, cooling the electroniccomponent. The elongated shape of the core allows for heat to be drawnprimarily normal to the printed circuit board. Thus, the cooling devicemay occupy minimal area, which allows a higher concentration ofelectronic components to be mounted to the printed circuit board.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a top perspective view of a cooling device having a pluralityof fin rings and a fan.

FIG. 2 is a top perspective view of the cooling device of FIG. 1 havinga single first fin ring and without the fan.

FIG. 3 is a side view of the cooling device of FIG. located adjacent aheat generating electronic device.

FIG. 4 is a top perspective view of a fin ring of the type illustratedin the cooling device of FIG. 2.

FIG. 5 is a top perspective view of the cooling device of FIG. 2 havinga second fin ring located adjacent the first fin ring.

FIG. 6 is a schematic illustration of the cooling device illustrated inFIG. 1.

FIG. 7 is a side view of the cooling device of FIG. 3 with a shroudattached thereto.

FIG. 8 is a top perspective view of the cooling device of FIG. 2 withthe addition of a compression ring.

FIG. 9 is a side view of the cooling device of FIG. 1 with a pluralityof compression rings attached thereto.

FIG. 10 is a top cutaway view of a cooling device having a ribbon-typecooling fin associated therewith.

FIG. 11 is the cooling device of FIG. 10 with the addition of a shroudencompassing the core and ribbon-type cooling fin.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 11, in general, illustrate a heat sink 200 for removingheat from a heat source 330. The heat sink 200 may comprise: at leastone first surface 216 adapted to contact at least a portion 332 of theheat source 330; a core member 210, wherein the at least one firstsurface 216 is located on the core member 210; at least one outerperipheral surface 212 located on the core member 210; and at least onecooling fin device 240 having at least one inner peripheral surface 248and at least one cooling fin 246 associated therewith. The at least oneinner peripheral surface 248 of the cooling fin device 240 may beadjacent the at least one outer peripheral surface 212 of the coremember 210.

FIGS. 1 through 11 also, in general, illustrate a method ofmanufacturing a heat sink 200. The method may comprise: providing a coremember 210 having at least one outer peripheral surface 212; providingat least one cooling fin device 240 having at least one inner peripheralsurface 248 and at least one cooling fin 246 associated therewith; andlocating the at least one inner peripheral surface 248 of the at leastone cooling fin device 240 adjacent the at least one outer peripheralsurface 212 of the core member 210.

FIGS. 1 through 11 also, in general, illustrate a heat sink 200 forremoving heat from a heat source 330. The heat sink 200 may comprise: atleast one first surface 216 adapted to contact at least a portion 332 ofthe heat source 330; a core member 210, wherein the at least one firstsurface 216 is located on the core member 210; an axis AA associatedwith the core member 210, wherein the axis AA is substantially normal tothe at least one first surface 216; at least one outer peripheralsurface 212 located on the core member 210; at least one cooling finlocated adjacent the at least one outer peripheral surface 212 of thecore member 210 and extending substantially radial and substantiallyaxial relative to the axis AA; and a shroud that substantiallyencompasses the at least one cooling fin and the core member 210.

Having generally described the cooling device 100, FIG. 1, it will nowbe described in greater detail. The cooling device 100 may have a fan110 associated with a heat sink 200. The following description describesthe heat sink 200 followed by a description of the fan 110. Adescription of the operation of the fan 110 associated with the heatsink 200 follows their individual descriptions.

Referring to FIG. 2, which shows a partially constructed heat sink 200,the heat sink 200 may have a core 210 with a first fin ring 281 locatedadjacent the core 210. For illustration purposes, FIG. 2 shows only asingle first fin ring 281 attached to the core 210. Further below inthis description, the heat sink 200 will be described having a pluralityof fin rings 240, FIG. 1, attached to the core 210. The first fin ring281 and other fin rings described herein are sometimes referred to ascooling fin devices.

The core 210 may be made of a thermally conductive material, such ascopper or aluminum. The core 210 may have a top portion 214 and a lowerportion 216 with a peripheral surface 212 located therebetween. The core210 may have a substantially cylindrical shape with a diameter D1. Aheight H1 may extend between the top portion 214 and the lower portion216. The diameter D1 may, as an example, be approximately 3.0centimeters and the height H1 may also, as an example be approximately3.0 centimeters. The diameter D1 and height H1, however, are dependenton the specific cooling application of the cooling device 100. Theperipheral surface 212 may have a perimeter, which in the case of theperipheral surface 212 illustrated herein, is the cylindrical peripheralsurface 212 having a diameter D1. The core 210 is illustrated herein asbeing cylindrical for illustration purposes, however, the core 210 mayhave other shapes. For example, the core 210 may be in the shape of acube, wherein the perimeter of a cube-shaped core is the boundarydefined by the sides of the cube.

Referring briefly to FIG. 3, which is a side view of the cooling device100 of FIG. 1, the lower portion 216 of the core 210 may be adapted tocontact a top surface 332 of a heat generating device 330. Morespecifically, the lower portion 216 may be adapted to provide themaximum thermal conductivity between the core 210 and the heatgenerating device 330. For example, in the situation where the heatgenerating device 330 is an integrated circuit, the top surface 332 ofthe integrated circuit is typically planar. Accordingly, the lowerportion 216 of the core 210 may be substantially planer and may have anarea that is approximately the same as the area of the top surface 332of the heat generating device 330.

Having described the core 210, the first fin ring 281 will now bedescribed. FIG. 4 is a top perspective view of the first fin ring 281separated from the core 210, FIG. 2, and is representative of theremaining fin rings 240 that may be located adjacent the core 210 asillustrated in FIG. 3. The first fin ring 281 may have a collar 244 witha plurality of cooling fins 246 attached thereto. The collar 244 mayhave an inner peripheral surface 248 having an upper ring portion 270and a lower ring portion 272. The upper portion 270 and the lowerportion 272 may be separated by a height H2, which may, as an example,be approximately 0.25 centimeters. The upper ring portion 270 and thelower ring portion 272 may be located on substantially parallel planes.A reference axis BB may pass through the mid point 274 of the collar 244and may be substantially normal to the planes defined by the upper ringportion 270 and the lower ring portion 272.

The inner peripheral surface 248 has a perimeter associated with it,which in the embodiment described herein is a cylindrical surfaceextending between the upper portion 270 and the lower portion 272. Theperimeter of the inner peripheral surface 248 may be substantiallysimilar to the perimeter a cylindrical portion of the surface 212, FIG.2, of the core 210. For example, the inner peripheral surface 248 may beround and may have a diameter D2 that is approximately the same as thediameter D1 of the core 210, FIG. 2. In one embodiment of the heat sink200, FIG. 2, the diameter D1 of the core 210 and the diameter D2, FIG.4, of the first fin ring 281 are appropriately sized so as to cause aninterference fit between the first fin ring 281 and the core 210 as isdescribed in greater detail below.

The collar 244 may have an outer surface 252 wherein the cooling fins246 are attached to the outer surface 252. Reference is made to a firstfin 250, which is representative of all the cooling fins 246 and theirassociation with the outer surface 252. The first fin 250 may have amounting portion 256, an end portion 258, a surface 260, an upper end262, and a lower end 264. The surface 260 may be defined by theboundaries of the mounting portion 256, the end portion 258, the upperend 262, and the lower end 264. The surface 260 may be substantiallyplanar, accordingly, the end portion 258 may be substantially linear. Alength D3 may extend between the mounting portion 256 and the endportion 258. The length D3 may, as an example, be approximately 11 to 13millimeters. A length D4 may extend between the upper end 262 and thelower end 264. It is preferable to maintain the length D4 relativelysmall in order to reduce the boundary layer of air that may accumulateon the surface 260 of the first fin 250 when air is forced past thesurface 260. The D4 may, as an example, be approximately 3.25millimeters. The mounting portion 256 may be a twisted portion of thefirst fin 250 and may serve to create an angle φ between the end portion258 and the reference axis BB. The angle φ may, as an example, beapproximately 45 degrees.

The collar 244 and the cooling fins 246 may be made of a heat conductingmaterial such as aluminum or copper. The junction between the collar 244and the mounting portion 256 of the cooling fins 246 may conduct heatwith minimal thermal resistance. For example, the collar 244 may beintegrally formed with the cooling fins 246 or they may be weldedtogether. In a non-limiting example of manufacturing the first fin ring281, the first fin ring 281 may be fabricated from a single metal sheet,such as a copper or aluminum sheet. The metal sheet may, as an example,have a thickness of approximately 15 to 20 thousandths of an inch.Fabrication of the first fin ring 281 may commence with stamping thecollar 244 out of the metal sheet. The collar 244 is essentially acircular cutout having a diameter D2 and a height H2. Accordingly, thestamping process forms the diameter D2 and the height H2 of the collar244. The cooling fins 246 may then be stamped out of the metal sheet.For example, the cooling fins 246 may be cut out of the metal sheet viaa conventional stamping process. The metal sheet may then be placed intoa dye that twists the cooling fins 246 at the mounting portion 256 inorder to form the angle φ.

Referring again to FIG. 2, the first fin ring 281 may be pressed ontothe core 210 in a conventional manner to form an interference fitbetween the first fin ring 281 and the core 210. The interference fit isa result of a cylindrical portion of the surface 212 of the core 210being substantially the same as the perimeter of the inner peripheralsurface 248, FIG. 4, of the first fin ring 281. Accordingly, thediameter D1 of the core 210 is substantially the same or slightly largerthan the diameter D2, FIG. 4, of the first fin ring 281. As shown inFIG. 2, the first fin ring 281 may be located in the vicinity of thelower portion 216 of the core 210. Referring to FIG. 5, which is theheat sink 200 of FIG. 2 with an additional fin ring attached thereto,after the first fin ring 281 has been pressed onto the core 210 a secondfin ring 282 may be pressed onto the core 210. The process of pressingfin rings 240 onto the core 210 may continue until the surface 212 ofthe core 210 is substantially covered with fin rings 240 as illustratedin FIG. 3.

FIG. 3 illustrates nine fin rings 240 affixed to the core 210. The finrings 240 are referred to individually as the first through the ninthfin rings and referenced numerically as 281 through 289 respectively.The plurality of fin rings 240 substantially increases the surface areaavailable on the heat sink 200 for convecting heat to the surroundingatmosphere. In addition, the fin rings 240 are relatively thin, whichincreases their ability to convect heat to the surrounding atmosphere byminimizing the air resistance through the fin rings 240 as is describedbelow. As illustrated in FIG. 3, the cooling fins 246 are substantiallyplanar and are located on planes that are substantially parallel to eachother. As described in greater detail below, the planar arrangement ofthe cooling fins 246 forms channels that serve to guide air past thecooling fins 246, which increases convection of heat to the surroundingatmosphere. The planar arrangement of the fin rings 240 is describedbelow with reference to the schematic illustration of FIG. 6.

Having described the heat sink 200, the fan 110 will now be describedfollowed by a description of the association between the heat sink 200and the fan 110.

Referring again to FIG. 3, the fan 110 may be a conventional electricfan. The fan 110 may, as an example, be of the type commerciallyavailable from the Matsushita Electric Corporation as Model FBA06T12Hand sold under the tradename PANAFLO. The fan 110 may have a rotatingportion 112, wherein the rotating portion 112 may have a top portion114, a lower portion, not shown in FIG. 3, and a peripheral side wall116. A reference axis AA may extend through the center of the topportion 114 and may be substantially normal to the top portion 114. Asdescribed in greater detail below, the reference axis AA may define acenter of rotation of the rotating portion 112. A direction 130 is usedherein to describe the rotational direction of the rotating portion 112about the reference axis AA.

The peripheral side wall 116 of the fan 110 may have a plurality ofcirculating fins 118 attached thereto. The circulating fins 118 may besubstantially identical to each other. A first circulating fin 119 isused as a reference to describe all the circulating fins 118. The firstcirculating fin 119 may have an inner side 120, FIG. 1, an outer side122, an upper side 124, and a lower side 126. The sides may define theboundaries of a surface 128. The inner side 120, FIG. 1, of the firstcirculating fin 119 may be attached to the peripheral side wall 116 ofthe rotating portion 112 in a conventional manner. For example, thefirst circulating fin 119 may be adhered to or integrally formed withthe side wall 116. The attachment of the first circulating fin 119 tothe side wall 116 may define an angles θ between the surface 128 and thereference axis AA. The angle θ may, as an example, be about 45 degrees.In a preferred embodiment, the angle θ is equal to 90 degrees minus theangle φ of FIG. 4. As described in greater detail below, the angle θ mayserve to determine the direction of air flow generated by the fan 110 asthe rotating portion 112 rotates in the direction 130.

Having described the fan 110 and the heat sink 200 separately, theirassociation with each other will now be described.

As illustrated in FIG. 3, the fan 110 may be located adjacent the topportion 214, FIG. 2, of the core 210. The fan 110 may, as examples, beattached to the core 210 by the use of fasteners, e.g., screws, or itmay be adhered to the core 210. It should be noted, however, that thefan 110 does not need to be physically attached to the core 210 and thatthe fan 110 only needs to be able to force air past the cooling fins246.

FIG. 6, which is a side schematic illustration of the fan 110 associatedwith the heat sink 200, illustrates the air flow between the fan 110 andthe heat sink 200. It should be noted that for illustration purposes theheat sink 200 illustrated in FIG. 6 only shows a limited number of finrings 240 and cooling fins 246. As described above, the firstcirculating fin 119 is positioned at an angle θ relative to thereference axis AA. The angle θ is described herein as beingapproximately 45 degrees. The cooling fins 246 are positioned at anangle φ relative to the reference axis AA, which is described herein asbeing approximately 45 degrees. A reference axis CC may extend parallelto the end portions 258 of the cooling fins 246 and may be substantiallyperpendicular to the surface 128 of the first circulating fin 119.Accordingly, the reference axis CC may be positioned at the angle θrelative to the reference axis AA. An air flow direction 290 commencesat the surface 128 of the first circulating fin 119 and extends parallelto the reference axis CC, which is normal to the surface 128. Asdescribed below, the air flow direction 290 is the direction that airflows as the first circulating fin 119 rotates in the direction 130.

When the rotating portion 112 rotates in the direction 130, the firstcirculating fin 119 forces air to circulate past the cooling fins 246.The airflow generated by the rotating first circulating fin 119 flows inthe air flow direction 290, which is parallel to the reference axis CC.The air flow direction 290 is, accordingly, parallel to the end portions258 and the surfaces 260 of the cooling fins 246. This relation betweenthe air flow direction 290 and the cooling fins 246 allows air generatedby the rotating first circulating fin 119 to pass over the surfaces 260of the cooling fins 246 with little resistance. In addition, this airflow direction 290 relative to the cooling fins 246 reduces any eddycurrents that may, in turn, reduce the air flow through the heat sink200. In addition, as described above, the cooling fins 246 are thinenough to minimize air resistance, but thick enough to transfer heatfrom the core 210. Thus, the cooling fins 246 cause little resistance tothe air flow through the heat sink 200, which in turn, allows for themaximum convection of heat from the cooling fins 246 to the surroundingatmosphere.

The thin cooling fins 246 and their placement relative to each otherallows them to be condensed or “nested” which in turn allows a greaternumber of cooling fins 246 to convect heat to the surroundingatmosphere.

In addition, the placement of the fin rings 240 and the cooling fins 246creates channels for air to flows past the cooling fins 246. One suchchannel is defined by the reference axis CC, which is parallel to theair flow direction 290. Other channels are parallel to the channeldefined by the reference axis CC. Accordingly, the channels allow air tobe able to be forced past the cooling fins 246 with minimal resistanceand with minimal creation of eddy currents.

Referring again to FIG. 3, having described the cooling device 100, itwill now be described cooling a heat generating device 330 that ismounted to a top surface 342 of a printed circuit board 340. The heatgenerating device 330 is described herein as being an integrated circuitthat generates heat when it is in use. The heat generating device 330may have a top surface 332 wherein most of the heat generated by theheat generating device 330 flows from the top surface 332 in a direction334. The cooling device 100 may be operatively associated with the heatgenerating device 330 so that the lower portion 216 of the core 210 isin thermal contact with the top surface 332 of the heat generatingdevice 330. In order to assure thermal conductivity between the heatgenerating device 330 and the cooling device 100, the cooling device 100may be attached to the printed circuit board 340 in a conventionalmanner.

When the heat generating device 330 is in use, it generates more heatthan it can dissipate alone. Heat accumulates in the top surface 332 ofthe heat generating device 330 and generally flows in the direction 334.The heat generated by the heat generating device 330 is absorbed intothe core 210 by virtue of the thermal contact between the top surface332 of the heat generating device 330 and the lower portion 216 of thecore 210. Thus, the temperature of the heat generating device 330 isreduced by the absorption of heat into the core 210. The heat absorbedby the core 210 dissipates to the surface 212 where some of the heat isconvected directly to the surrounding atmosphere. The interference fitsbetween the fin rings 240 and the core 210 cause the majority of theheat dissipated to the surface 212 of the core 210 to transfer to thefin rings 240 and into the cooling fins 246.

Simultaneous to heat being absorbed into the core 210 and dissipated tothe cooling fins 246, the fan 110 forces air to flow in the air flowdirection 290 past the surfaces 260 of the cooling fins 246. Morespecifically, the fan 110 may draw air into the cooling device 100 alongan air flow direction 360. The air passes through the heat sink 200 inthe air flow direction 290 and is exhausted along an air flow direction362. Accordingly, the heat in the cooling fins 246 is convected into thesurrounding atmosphere.

The rate of heat transfer between the core 210 and the cooling fins 246is directly proportional to the temperature difference between thecooling fins 246 and the surface 212 of the core 210. Likewise, the heattransfer from the heat generating device 330 to the core 210 is directlyproportional to the temperature of the core 210. Accordingly, a higherrate of heat transfer from the heat generating device 330 can beaccomplished by significantly cooling the cooling fins 246. Thetemperature of the cooling fins 246 is proportional to their positionrelative to the heat generating device 330, wherein the cooling fins 246positioned close to the heat generating device 330 are hotter than thosepositioned further from the heat generating device 330. By forcingrelatively cool air in the air flow direction 290, all the cooling fins246 are exposed to relatively cool air, which reduces their temperature.The relatively cool cooling fins 246 are able to transfer heat from thesurface 212 of the core 210 at an increased rate, which in turn, coolsthe core 210 at an increased rate. The cooler core 210 is, thus, able toremove more heat at a higher rate from the heat generating device 330.If, on the other hand, the air flow direction 290 is opposite thatillustrated herein, the cooling fins 246 located on the fin rings 240above the first fin ring 281 would be cooled by air that had convectedheat from the first fin ring 281, which is the hottest of the fin rings240. The remaining fin rings 240 would, thus, be heated by the heatconvected from the first fin ring 281. This heating reduces the coolingcapability of the heat sink 200, however, some applications of thecooling device 100 may require the air flow in this direction.

Due to inherent air restrictions in the heat sink 200 caused by thecooling fins 246, not all the air forced into the heat sink 200 by thefan 110 passes by the cooling fins 246. For example, the fan 110 maycause air pressure to build up in the cooling fins 246, which in turn,causes some air to leave the heat sink 200 without passing by all thefin rings 240. The heat sink 200 of FIG. 3 shows that some air mayfollow an air flow direction 370 and may be exhausted from the heat sink200 without passing by all of the cooling fins 246. Accordingly, the airfollowing the air flow direction 370 is not used efficiently.

Referring to FIG. 7, in order to assure all the air drawn into thecooling device 100 passes the cooling fins 246, a shroud 350 may beadded to the cooling device 100. The shroud 350 may, as an example, be aduct that fits over the heat sink 200 and does not allow air to escapefrom the heat sink 200 until it has passed by all the cooling fins 246.Thus, all the air entering the cooling device 100 along the air flowdirection 360 is exhausted from the cooling device 100 along the airflow direction 362. Accordingly, the efficiency of the cooling device100 is significantly improved.

The shroud 350 may have an upper portion 352 and a lower portion 354.The upper portion 352 may substantially encompass the fan, not shown,and the lower portion 354 may substantially encompass the heat sink 200.A plurality of openings 356 may be formed into the upper portion 352 inorder to facilitate air flow through the cooling device 100. Morespecifically, air may flow in an air flow direction 364 through theopenings 356 where it joins the air flowing along the air flow direction360. Accordingly, the openings 356 may serve to increase the volume ofair that passes the cooling fins 246, which in turn increases theconvection of heat to the surrounding atmosphere. The shroud 350 isillustrated as having slots 364 that are vertical, however, the slots364 may be slanted to correlate with the angle of the first circulatingfin 119, FIG. 3. The slots 364 may also be slanted so as to correlatewith the air flow generated by the fan 110, FIG. 1.

Having described an embodiment of the cooling device is 100, otherembodiments of the cooling device 100 will now be described.

Referring again to FIG. 5, the cooling device 100 has been describedhere as having the fin rings 240 pressed onto the core 210. Pressing thefin rings 240 onto the core 210 creates interference fits between thefin rings 240 and the core 210, which provide for high thermalconductivity between the core 210 and the fin rings 240. Theinterference fits, however, require that the core 210 and the fin rings240 be manufactured to precise specifications. If precise manufacturingspecifications are not achieved, the fin rings 240 may be loose on thecore 210 or the fin rings 240 may not be able to be pressed onto thecore 210.

Referring to FIG. 8, the above-described problems of controlling thespecifications of the fin rings 240, FIG. 3, may be overcome by theaddition of compression rings pressed onto the core 210. In thisembodiment of the heat sink 200, interference fits between the fin rings240 and the core 210 are not required. A compression ring 380 may abutthe top side of the first fin ring 281. A second compression ring, notshown, may abut the bottom side of the first fin ring 281. Thecompression ring 380 may be a ring of thermally conductive material,such as copper or aluminum, that is pressed onto the core 210 and firmlyabuts the first fin ring 281. Heat in the core 210 may then betransferred to the first fin ring 281 via the compression ring 380.Accordingly, the use of the compression ring 380 permits the first finring 281 to be manufactured to looser specifications than thosedescribed above.

A plurality of compression rings, not shown in FIG. 8 may be pressedonto the core 210 during the manufacturing process of the heat sink 200.For example, one compression ring, not shown in FIG. 8, may be pressedonto the core 210 in the vicinity of the lower portion 216. The firstfin ring 281 may then be placed over the core 210 so as to abut thecompression ring located in the vicinity of the lower portion 216. Thecompression ring 380 may then be pressed onto the core 210 so as to abutthe first fin ring 281. Accordingly, the first fin ring 281 issandwiched between compression rings. The compression rings may then beforced together to so that the first fin ring 281 is tightly compressedbetween them. This compression serves to enhance the thermalconductivity between the compression rings and the first fin ring 281,which in turn enhances the cooling capability of the heat sink 200.

Referring to FIG. 9, a plurality of compression rings may be pressedonto the core 210. The heat sink 200 illustrated in FIG. 9 is similar tothe heat sink 200 illustrated in FIG. 3, however, the heat sink 200 ofFIG. 9 has a plurality of compression rings pressed onto the core 210.The heat sink 200 may have a top compression ring 390 located in thevicinity of the top portion 214 of the core 210. The heat sink 200 mayalso have a bottom compression ring 392 located in the vicinity of thelower portion 216 of the core 210. A plurality of inner compressionrings 394 may be pressed onto the core 210, wherein one innercompression ring 394 is located between each of the fin rings 240.

The heat sink 200 of FIG. 9 may be manufactured by first pressing thetop compression ring 390 onto the core 210. The ninth fin ring 289 maythen be slipped over the core 210 and placed near the top compressionring 390. An inner compression ring 394 may then be pressed onto thecore so as to sandwich the ninth fin ring 289 between compression rings.The eighth fin ring 288 may then be slipped over the core 210 to abutthe previously pressed on inner compression ring 394. The process ofalternating fin rings 240 and inner compression rings 394 continuesuntil all of the fin rings 240 have been placed onto the core 210.Accordingly, an inner compression ring 394 is located between each finring 240. The bottom compression ring 392 may then be pressed onto thecore 210. In order to assure that thermal contact exists between the finrings 240 and the compression rings 390, 392, 394, the top compressionring 390 and the bottom compression ring 392 may be pressed together.This will cause the fin rings 240 to contact all the compression rings390, 392, 394, which increases the thermal conductivity between thesurface 212 of the core 210 and the fin rings 240.

Referring again to FIG. 3, in one embodiment of the cooling device 100,the core 210 may be a heat pipe or have a heat pipe located therein. Aheat pipe is a device that is known in the art and serve to rapidlytransfer heat. Thus, the interior of the core 210 may be a partiallyevacuated chamber containing a small amount of a liquid. When the core210 is cool, the liquid is located in the vicinity of the lower portion216 of the core 210. The liquid evaporates when it is heated by the heatgenerating device 330. The vapor from the evaporated liquid condenses onthe sides of the core 210 and, thus, transfers its heat to the sides ofthe core 210. The heat may then quickly transfer to the surface 212 ofthe core 210. The heat may then be convected to the surroundingatmosphere as described above. The use of the heat pipe substantiallyincreases the heat transfer through the core 210, which in turnincreases the cooling capability of the cooling device 100. Examples ofheat pipes are disclosed in the following United States patents andpatent applications, which are all hereby incorporated by reference forall that is disclosed therein: Ser. No. 09/376,627 of Wagner et al. forCOOLING APPARATUS FOR ELECTRONIC DEVICES; registration number U.S. Pat.No. 5,694,295 of Masataka et al. for HEAT PIPE AND PROCESS FORMANUFACTURING THE SAME.

The heat sink 200 has been described herein as having a plurality ofcooling fins 246 that extend radially from the core 210. Anotherembodiment of the heat sink 200 is illustrated in FIG. 10 and uses aribbon-type cooling fin, which is sometimes referred to herein as acooling ribbon 400. The cooling ribbon 400 may, as an example, beconstructed from a single piece of a thermally conductive material, suchas a sheet of copper or aluminum. Alternatively, the cooling ribbon 400may be extruded in a conventional manner. The cooling ribbon 400 mayhave a plurality of contact portions 410 and end portions 412. Thecontact portions 410 may serve to contact the surface 212 of the core210 and may, thus, be points where heat is transferred from the core 210into the cooling ribbon 400. The end portions 412 may be portions of thecooling ribbon 400 that are located furthest from the surface 212 of thecore 210. A plurality of inner air channels 420 may be located betweenthe surface 212 of the core 210 and the end portions 412. A plurality ofouter air channels 422 may be located between the contact portions 410and the cooling ribbon 400.

The cooling ribbon 400 may be pressed onto the core 210 in aconventional manner. For example, in one embodiment of the heat sink200, a single cooling ribbon 400 is pressed onto the core 210 andextends at least a portion of the length of the core 210. In anotherembodiment of the heat sink 200, a plurality of cooling ribbons 400 arepressed onto the heat sink 200 and extend at least a portion of thelength of the core 210. Heat in the surface 212 of the core 210transfers to the cooling ribbon 400 via the contact portions 410 whereit is convected into the surrounding atmosphere. The fan, not shown inFIG. 10, may force air in the inner air channel 420 and the outer airchannel 422 to increase the convection of the heat in the inner airchannel 420 to the surrounding atmosphere. Air will also pass in theouter air channel 422, however, much of this air may exit the outer airchannel 422 before it passes the length of the cooling ribbon 400.

In order to improve the efficiency of the cooling device 100, the shroud350 may be placed over the heat sink 200 as was described above and asis illustrated in FIG. 11. The shroud 350 forces air in the outer airchannel 422 to remain in the outer air channel 422 throughout the lengthof the shroud 350, which may be substantially similar to the length ofthe cooling ribbon 400. Accordingly, air in the outer air channel 422 isused more efficiently, which improves the overall efficiency of thecooling device 100.

In another embodiment of the heat sink 200, the cooling fins extendaxially and radially along the core 210 similar to the ribbon-typecooling fin 400 of FIG. 10. More specifically, the fins may extendsubstantially axially and radially relative to the reference axis AA asillustrated in FIG. 1. The axially and radially extending cooling finsallow the cooling fins and the core 210 to be extruded as a singlepiece. Accordingly, heat transfer between the core 210 and the axiallyextending cooling fins is maximized. As with the other embodiments ofthe cooling device 100, a shroud may substantially encompass the core210 and the cooling fins.

Referring again to FIG. 3, the fin rings 240 have been described asbeing adjacent to the surface 212 of the core 210. It is to beunderstood that the fin rings 240 may be attached to the core bynumerous methods. For example, the fin rings 240 may be pressed onto thecore 210. In another example, the core fin rings 240 may be soldered orbrazed to the core 210.

While an illustrative and presently preferred embodiment of theinvention has been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed and that the appended claims are intended to be construed toinclude such variations except insofar as limited by the prior art.

What is claimed is:
 1. A heat sink for removing heat from a heat source,said heat sink comprising: at least one first surface adapted to contactat least a portion of said heat source; a core member, wherein said atleast one first surface is located on said core member; at least oneouter peripheral surface located on said core member; at least onecooling fin device having at least one inner peripheral surface and atleast one cooling fin associated therewith, wherein said at least oneinner peripheral surface of said cooling fin device is adjacent said atleast one outer peripheral surface of said core member; and a shroudcomprising a first portion and a second portion, wherein said firstportion is located adjacent said at least one cooling fin, and whereinsaid second portion extends beyond said core member.
 2. The heat sink ofclaim 1 wherein said second portion of said shroud has at least one slotformed therein.